Control device for machine tool and machine tool

ABSTRACT

A control device for a machine tool and a machine tool capable of easily performing cutting with vibration according to the amount of feed is provided. The control device includes a control section for controlling the relative rotation and feeding of a cutting tool and a material, the control section performing cutting with vibration of the cutting tool relative to the material by combining a forward feed movement in the machining direction, in which the cutting tool machines the material, and a return movement in the counter-machining direction. A return movement setting section sets a pulse-like signal including a command for moving a cutting tool in the machining direction and a command for the return movement. A forward feed setting section makes the cutting tool reach a change point by combining the movement in the machining direction on the basis of the return movement setting section and the forward feed movement. A pulse-like signal is formed in sine waveform with an inflection point, and a phase of the inflection point for making the cutting tool reach the change point is set to a value different from a phase of the change point.

TECHNICAL FIELD

The present invention relates to a control device for a machine tool anda machine tool.

BACKGROUND ART

For example, Patent Literature 1 discloses a technique in vibrationcutting that includes a feeding means for feeding a relatively rotatingcutting tool and material, and the cutting tool is reciprocated relativeto the material and chips can be segmented in cutting the material bycombining a forward feed movement in the machining direction, in whichthe cutting tool machines the material, and a return movement in thecounter-machining direction different from the machining direction.

CITATION LIST Patent Literature

[Patent Literature 1] Japanese Patent Application Laid-Open No. 48-52083

SUMMARY OF INVENTION Technical Problem

In the vibration cutting described in Patent Literature 1, when thecutting tool returns in the counter-machining direction in thereciprocal movement, there is a problem that it is not easy to performthe vibration cutting with considering the return movement of thecutting tool to a predetermined position, which corresponds to apredetermined amount of feed of the cutting tool.

The present invention has been made in view of the above-describedproblem, and an object of the present invention is to provide a controldevice for a machine tool and a machine tool capable of easilyperforming cutting with vibration according to the amount of feed.

Solution to Problem

Firstly, the present invention is characterized in that a control devicefor a machine tool comprises: a feeding means for feeding a relativelyrotating cutting tool and material; and a control means for controllingthe rotation and operation of the feeding means, the control meansperforming control such that cutting is performed with vibrating thecutting tool relative to the material by combining a forward feedmovement in the machining direction, in which the cutting tool machinesthe material, and a return movement in the counter-machining directiondifferent from the machining direction, wherein the control deviceincludes: a return position calculation means for calculating a returnposition of the cutting tool at time when one vibration is completed onthe basis of the number of vibrations and an amount of feed that arepredetermined for one rotation of the cutting tool or the material; aforward feed setting means for setting the forward feed movement on thebasis of a change point setting value that determines a change pointfrom the machining direction to the counter-machining direction; and formaking the cutting tool reach the determined change point, and a returnmovement setting means for setting a pulse-like signal that is output asa command for the return movement so that the cutting tool reaches thecalculated return position at time when one vibration is completed, andwherein the return movement setting means sets a pulse-like signalincluding a command for moving a cutting tool in the machining directionand a command for the return movement, and the forward feed settingmeans makes the cutting tool reach the change point by combining themovement in the machining direction on the basis of the return movementsetting means and the forward feed movement, the pulse-like signal isformed in sine waveform with an inflection point, and a phase of theinflection point for making the cutting tool reach the change point isset to a value different from a phase of the change point.

Secondly, it is characterized in that the number of vibrations is one ormore.

Thirdly, it is characterized in that the number of vibrations is lessthan one.

Fourthly, it is characterized in that a machine tool comprises any oneof the above-described control devices for a machine tool.

Advantageous Effects of Invention

The present invention can provide the following effects.

-   (1) the cutting tool can be fed with the vibration by combining the    forward feed movement and the return movement. In particular, by the    return position calculation means, the forward feed setting means    and the return movement setting means, the vibration of the cutting    tool can be automatically set according to the predetermined amount    of feed. Thus, it is possible to easily perform cutting with the    vibration according to the amount of feed. The pulse-liked signal    can be formed in sine waveform as a command for both of the movement    in the machining direction and the return movement.

Further, if the phase of the inflection point in the pulse-liked signalis set to the same value as the phase of the change point, in the rootof the cutting tool, the position of the change point, at which themovement direction of the cutting tool is switched from the machiningdirection to the counter-machining direction, may be displaced. However,by setting the phase of the inflection point in the sine waveform to avalue different from the phase of the change point corresponding to thisinflection point, the cutting tool can reach the change point at apredetermined phase, and the root of the cutting tool, in which themachining direction is switched at the change point in a sine curve, canbe obtained.

-   (2) Vibration cutting in which the cutting tool or the material    vibrates once or more during one rotation of the material or the    cutting tool can be performed.-   (3) Vibration cutting in which the material or the cutting tool    rotates once or more during one vibration of the cutting tool or the    material can be performed.-   (4) A machine tool capable of easily performing cutting with the    vibration according to the amount of feed can be provided.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram of a machine tool according to an exampleof the present invention.

FIG. 2 is a block diagram of a control device.

FIG. 3 is a diagram illustrating the reciprocal movement and theposition of a cutting tool.

FIG. 4 is a diagram illustrating the routes of the cutting edge of thenth rotation, the n+1th rotation and the n+2th rotation of a spindle.

FIG. 5 is a diagram illustrating the vibration waveform of the referenceexample 1.

FIG. 6A is a diagram illustrating the generation of the vibrationwaveform of the reference example 1.

FIG. 6B is a diagram illustrating the generation of the vibrationwaveform of the reference example 1.

FIG. 6C is a diagram illustrating the generation of the vibrationwaveform of the reference example 1.

FIG. 6D is a diagram illustrating the generation of the vibrationwaveform of the reference example 1.

FIG. 7A is a diagram illustrating the generation of the vibrationwaveform of the reference example 1.

FIG. 7B is a diagram illustrating the generation of the vibrationwaveform of the reference example 1.

FIG. 8 is a diagram illustrating the vibration waveform of the referenceexample 2.

FIG. 9A is a diagram illustrating the generation of the vibrationwaveform of the reference example 2.

FIG. 9B is a diagram illustrating the generation of the vibrationwaveform of the reference example 2.

FIG. 9C is a diagram illustrating the generation of the vibrationwaveform of the reference example 2.

FIG. 9D is a diagram illustrating the generation of the vibrationwaveform of the reference example 2.

FIG. 10A is a diagram illustrating the generation of the vibrationwaveform of the reference example 2.

FIG. 10B is a diagram illustrating the generation of the vibrationwaveform of the reference example 2.

FIG. 11A is a diagram illustrating the vibration waveform of thereference example 3.

FIG. 11B is a diagram illustrating the vibration waveform of thereference example 3.

FIG. 11C is a diagram illustrating the vibration waveform of thereference example 3.

FIG. 12A is a diagram illustrating the vibration waveform of the presentexample.

FIG. 12B is a diagram illustrating the vibration waveform of the presentexample.

FIG. 12C is a diagram illustrating the vibration waveform of the presentexample.

DESCRIPTION OF EMBODIMENTS

Hereinafter, a control device for a machine tool and a machine toolaccording to the present invention will be described with reference tothe drawings. As shown in FIG. 1, a machine tool 100 includes a spindle110, a cutting tool 130 such as a tool bit for machining a workpiece W,and a control device 180.

A chuck 120 is provided at the end of the spindle 110, and the workpieceW is held by the spindle 110 via the chuck 120. The spindle 110 isrotatably supported by a spindle headstock 110A and rotationally drivenby the power of a spindle motor (for example, a built-in motor) providedbetween the spindle headstock 110A and the spindle 110, for example. Thespindle headstock 110A is installed on a Z-axis direction feedingmechanism 160.

The Z-axis direction feeding mechanism 160 includes a base 161 integralwith a bed, and a Z-axis direction guide rail 162 slidably supporting aZ-axis direction feeding table 163. When the Z-axis direction feedingtable 163 is moved by the drive of a linear servomotor 165 along theZ-axis direction shown in the figure which coincides with the rotationalaxis direction of the workpiece W, the spindle headstock 110A moves inthe Z-axis direction. The linear servomotor 165 has a mover 165 a and astator 165 b. The mover 165 a is provided on the Z-axis directionfeeding table 163, and the stator 165 b is provided on the base 161.

The cutting tool 130 is mounted on a tool post 130A, and the tool post130A is installed on an X-axis direction feeding mechanism 150.

The X-axis direction feeding mechanism 150 includes a base 151 integralwith a bed, and an X-axis direction guide rail 152 slidably supportingan X-axis direction feeding table 153. When the X-axis direction feedingtable 153 moves along the X-axis direction orthogonal to the Z-axisdirection shown in the figure by the drive of a linear servomotor 155,the tool post 130A moves in the X-axis direction. The linear servomotor155 has a mover 155 a and a stator 155 b. The mover 155 a is provided onthe X-axis direction feeding table 153, and the stator 155 b is providedon the base 151.

A Y-axis direction feeding mechanism may be provided in the machine tool100. The Y-axis direction is a direction orthogonal to the Z-axisdirection and the X-axis direction shown in the figure. The Y-axisdirection feeding mechanism may have the same structure as the Z-axisdirection feeding mechanism 160 or the X-axis direction feedingmechanism 150. As is conventionally known, the cutting tool 130 can bemoved in the Y-axis direction in addition to the X-axis direction by acombination of the X-axis direction feeding mechanism 150 and the Y-axisdirection feeding mechanism.

Although the Z-axis direction feeding mechanism 160, the X-axisdirection feeding mechanism 150 and the Y-axis direction feedingmechanism have been described with an example using a linear servomotor,a known ball screw and servomotor may be used.

The rotation of the spindle 110, the movement of the Z-axis directionfeeding mechanism 160 and the like are controlled by the control device180.

As shown in FIG. 2, the control device 180 includes a control section181, a numerical value setting section 182, and a storage section 183,which are connected via a bus.

The control section 181 is composed of a CPU or the like, loads variousprograms and data which are stored in, for example, a ROM of the storagesection 183 into a RAM, and executes the program. Thereby, the operationof the machine tool 100 can be controlled on the basis of the program.

The control section 181 has a motor control section 190 that is capableof controlling the rotation of the spindle 110 and the feed of theZ-axis direction feeding mechanism 160 and controls the operation ofeach motor.

In the example in FIG. 1, the control device 180 drives the spindlemotor to rotate the workpiece W relative to the cutting tool 130, drivesthe Z-axis direction feeding mechanism 160 to move the workpiece Wrelative to the cutting tool 130 in the Z-axis direction, and drives theX-axis direction feeding mechanism 150 to move the cutting tool 130relative to the workpiece W in the X-axis direction. The cutting tool130 is moved relative to the workpiece W with a relative movementbetween the cutting tool 130 and the workpiece W, and the cutting tool130 is fed relative to the workpiece W in a predetermined feed directionso that the workpiece W can be machined by the cutting tool 130.

As shown in FIG. 3, the control device 180 moves the cutting tool 130relative to the workpiece W along the feed direction by a predeterminedamount of the forward movement toward the machining direction, which isthe advancing direction of the machining feed, (this movement isreferred to as forward movement), and then the Z-axis direction feedingmechanism 160 or the X-axis direction feeding mechanism 150 is driven tomove the cutting tool 130 by a predetermined amount of backward movementtoward the counter-machining direction, which is the opposite directionto the machining direction (this movement is referred to as backwardmovement). The control section 181 moves the Z-axis direction feedingmechanism 160 or the X-axis direction feeding mechanism 150 to move thespindle headstock 110A or the tool post 130A so that the cutting tool130 reciprocates and vibrates relative to the workpiece W. Then, thecutting tool 130 can be fed relative to the workpiece W by a difference(an amount of progression) between the amount of the forward movementand the amount of the backward movement. When the outer periphery of theworkpiece W is cut by the cutting tool 130, the circumferential surfaceof the workpiece W is machined in a waveform according to the phase ofthe spindle 110.

The total amount of progressing movement while the phase of the spindlechanges from 0 degree to 360 degrees, which is one rotation of theworkpiece W, is the amount of feed F of the cutting tool. The number ofreciprocal movements of the cutting tool 130 in one rotation of theworkpiece W is the number of vibration D. FIG. 4 shows an example inwhich the number of vibrations D is 1.5 (times/r). A virtual line(dashed line) passing through the valley of the waveform is a feedstraight line indicating the amount of feed, and a position where thephase of the spindle is 360 degrees in the feed straight linecorresponds to the amount of feed F per one rotation of the workpiece W.

Since the number of vibrations D is not an integer, the route of thecutting edge of the cutting tool 130 in the nth rotation of the spindle110 (or workpiece W) (indicated by a solid line in FIG. 4) and the routeof the cutting edge in the n+1th rotation (indicated by a broken line inFIG. 4) shift in the direction of the phase of the spindle (horizontalaxis direction of the graph in FIG. 4), and the routes of the cuttingedge of the cutting tool 130 overlaps while cutting the workpiece W.

In the overlap period of the routes of the cutting edge in which theroute of the cutting edge of the n+1th rotation is included in the routeof the cutting edge of the nth rotation, portions to be machined in theworkpiece W has already been machined by the machining of the nthrotation. Therefore, the cutting tool 130 and the workpiece W do notcontact in the feed direction. Thus, there is an air-cut period in whichthe cutting tool 130 substantially does not machine the workpiece W, andchips generated on the workpiece W are divided into segmented chips. Thecutting tool 130 machines the workpiece W while vibrating by beingreciprocated relative to the workpiece W. This vibration cutting makesit possible to machine the workpiece W smoothly with segmenting chips.

In the example in FIG. 4, the nth route of the cutting edge and then+1th route of the cutting edge are reversed by 180 degrees. The air-cutperiod can be obtained if the nth route of the cutting edge and the n+1route of the cutting edge do not coincide with each other (are not inthe same phase), and it is only necessary that the nth route of thecutting edge and the n+1th route of the cutting edge shift in the phasedirection of the spindle.

However, if the amount of feed F is increased while maintaining theconstant amplitude, the period in which the route of the cutting edge ofthe n+1th rotation is included in the route of the cutting edge of thenth rotation decreases. If the route of the cutting edge of the n+1throtation does not reach the route of the cutting edge of the nthrotation, the air-cut period will not be obtained.

The period in which the route of the cutting edge of the n+1th rotationis included in the route of the cutting edge of the nth rotation changesin accordance with the amount of feed F and the amplitude of thevibration waveform. Therefore, the control section 181 is configured toset the amplitude of the vibration waveform in proportion with theamount of feed F so that the air-cut period is obtained. For performingthe cutting, the number of rotations of the spindle and the amount offeed F are specified in advance for example by specifying them in amachining program. An amplitude ratio with respect to the amount of feedF is defined as an amplitude feed ratio Q. The control section 181 isconfigured to set the amplitude to Q*F, which is a multiplication of theamount of feed F and the amplitude feed ratio Q. The amplitude feedratio Q can be specified as a value following Q (argument Q), forexample, in a machining program. Similarly, the number of vibrations Dcan also be specified as a value following D (argument D) in themachining program.

The control section 181 has a return position calculation section 191, aforward feed setting section 192 and a return movement setting section193 in order to move the cutting tool 130 relative to the workpiece Wwith vibrating the cutting tool 130. The control section 181 correspondsto the control means of the present invention, and the return positioncalculation section 191, the forward feed setting section 192, and thereturn movement setting section 193 correspond to the return positioncalculation means, the forward feed setting means and the returnmovement setting means of the present invention respectively.

When the amount of feed F is specified, a feed straight line isdetermined as shown in FIG. 5. Hereinafter, the feed straight line isreferred to as a substantial feed line G. In a case where the number ofvibrations D is 1.5 (times/r), the substantial feed lined G is indicatedby a dashed line in the graph in FIG. 5. In the graph, the phase of thespindle 110 is set as the horizontal axis direction and the position ofthe cutting tool 130 in the feed direction is set as the vertical axis.The cutting tool 130 is fed relative to the workpiece W so that thecutting tool 130 reaches the substantial feed line G at the time whenone vibration is completed, the movement thereof switches from thebackward movement to the forward movement, and the cutting tool 130vibrates 1.5 times during one rotation of the workpiece W, in otherwords vibrates 3 times during two rotation of the workpiece W.

On the basis of the number of vibrations D and the amount of feed F, thereturn position calculation section 191 calculates a position on thesubstantial feed line G, at which the cutting tool 130 is located at thetime when one vibration is completed, as a return position.

FIG. 5 shows return positions for three vibrations as direction changepoints B1, B2 and B3 where the movement switches from the backwardmovement to the forward movement. The vibration waveform in FIG. 5 isexpressed on a workpiece basis, and return positions of the cutting tool130 at the time when one vibration is completed are on a substantialfeed line G indicated by a dashed line in FIG. 6A. The phase of thespindle at the return position of the cutting tool 130 is obtained bymultiplying the angle of one rotation of the workpiece W (360 degrees)by the inverse number (⅔) of the number of vibrations D. As shown inFIG. 6B, in the reference example 1, the change point B1 is at aposition where the phase of the spindle is 240 degrees. Thereafter, theposition of each change point is on the substantial feed line G, andintervals between change points are determined by multiplying the angleof one rotation of the workpiece W by the inverse number of the numberof vibrations D. In the reference example 1, the change point B2 on thesubstantial feed line G is at a position where the phase of the spindleis 480 degrees, and the change point B3 is at a position where the phaseof the spindle is 720 degrees. The return position calculation section191 can calculate each return position on the basis of the amount offeed F and the number of vibrations D as described above.

On the other hand, the amplitude is set by multiplying the amount offeed F by the amplitude feed ratio Q. Therefore, the direction changepoint A1, at which the forward movement switches to the backwardmovement, is on a straight line (amplitude line QF) that is obtained byoffsetting the actual feed line G by the amplitude Q*F. In the case ofthe reference example 1, the phase of the spindle at the change point A1is 120 degrees, which is a phase of the spindle obtained by multiplying240 degrees, which is the phase of the spindle at the change point B1,by the inverse number (½) of the numerator of the inverse number (⅔) ofthe number of vibrations D. As shown in FIG. 6B, the change point A1 isset from the intersection of the amplitude line QF and the vertical linepassing through 120 degrees of the phase of the spindle. Thereafter, theposition of each change point A is on the amplitude line QF, and on anintermediate angle between the angles of change points B adjoining thechange point A. For example, in the case of the reference example 1, thechange point A2 is at an intermediate position (where the phase of thespindle is 360 degrees) from 240 degrees, which is the phase of thespindle of the change point B1, to 480 degrees, which is the phase ofthe spindle of the change point B2, and the change point A3 is at anintermediate position (where the phase of the spindle is 540 degrees)from 480 degrees, which is the phase of the spindle of the change pointB2, to 720 degrees, which is the phase of the spindle of the changepoint B3. As described above, the change point A1 is determined usingthe amount of feed F, the amplitude feed ratio Q, and the number ofvibrations D as parameters (change point setting values). The forwardfeed setting section 192 sets a straight line passing through the 0degree of the phase of the spindle and the change point A1 as forwardfeed movement, and the control section 181 outputs a forward feedcommand for moving the cutting edge along the forward feed movement.

The return movement setting section 193 is configured to output amovement command for moving the cutting tool 130 in thecounter-machining direction as a pulse-like signal P at a predeterminedinterval. As shown in FIG. 6C, the direction change point B1 is at aposition where the phase of the spindle is 240 degrees. Therefore, thepulse-like signal P has a downwardly convex waveform (indicated by atwo-dot chain line in FIG. 6C) opposite to the feed direction (verticalaxis direction in the graph in FIG. 6C) so that the cutting edge returnsfrom the change point A1 to the change point B1. The pulse-like signal Pis set as a signal output as a movement command for moving the cuttingtool 130 in the counter-machining direction.

In response to the pulse-like signal P, a return movement, in which thecutting edge periodically moves in the counter-machining direction, isperformed. The height of the convex shape of the pulse-like signal P canbe determined according to the distance between A1 and B1 viewed in thefeed direction. The pulse-like signal P is set so that, by combining theforward feed movement and the return movement, the cutting edge performsa backward movement F″ that connects the change point A1 and the changepoint B1 as shown in FIG. 6D. And the return movement setting section193 is configured to include the pulse-like signal P.

The pulse-like signal of the movement command for moving the cuttingtool 130 in the counter-machining direction, which is a periodicpulse-like command from the return movement setting section 193, has aperiod so that the backward movement F″ is started from each changepoint A. First, at the timing when the phase of the spindle is 120degrees, the cutting edge starts the backward movement F″ from thechange point A1 to the change point B1 (a position where the phase ofthe spindle is 240 degrees) by the command of moving in thecounter-machining direction (the downwardly convex portion of thepulse-like signal).

On the other hand, if there is no command of moving in thecounter-machining direction from the return movement setting section193, the cutting edge simply moves from the change point B to the changepoint A along the forward feed movement. Therefore, as shown in FIG. 7A,a forward movement F′ from the change point B1 to the change point A2 (aposition where the phase of the spindle is 360 degrees) is performed.

Next, the movement in the counter-machining direction is commanded atthe timing when the phase of the spindle is 360 degrees, and a backwardmovement F″ passing through the change point A2 and the change point B2(a position where the phase of the spindle is 480 degrees) is performed.When the change point A1 and the change point B2 coincide with eachother, the air-cut occurs and the chip is segmented.

The above operation is repeated, and as shown in FIG. 7B, the forwardmovement F′ passing through the change point B2 and the change point A3(a position where the phase of the spindle is 540 degrees) and thebackward movement F″ passing through the change point A3 and the changepoint B3 (a position where the phase of the spindle is 720 degrees) areperformed. When the change point A2 and the change point B3 coincidewith each other, the chip is segmented.

As described above, the cutting tool 130 can be fed with theabove-mentioned vibration by combining the forward feed movement and thereturn movement. In particular, by the return position calculationsection 191, the forward feed setting section 192 and the returnmovement setting section 193, the vibration of the cutting tool 130 canbe automatically set according to the predetermined amount of feed F.Thus, it is possible to easily perform cutting with the vibrationaccording to the amount of feed F.

The number of vibrations D can be set to be less than one. FIG. 8 showsan example in which the number of vibrations D is 0.5 (times/r). Forperforming this cutting, the number of rotations of the spindle and theamount of feed F are also specified in advance for example by specifyingthem in a machining program.

When the amount of feed F is specified, as shown in FIG. 8, asubstantial feed line G is determined (indicated by a dashed line inFIG. 8). The cutting tool 130 reaches the substantial feed line G whenone vibration is completed, and the movement thereof switches frombackward movement to forward movement.

In the example of the graph shown in FIG. 8, the phase of the spindle110 is set as the horizontal axis direction and the position in the feeddirection of the cutting tool 130 is set as the vertical axis. In theexample, the cutting tool 130 vibrates one time while the spindle 110performs multiple rotation (two rotation in this example). In themovement route of the cutting tool 130, the forward movement and thebackward movement are performed at the same speed. The cutting tool 130advances with forward movement in the first rotation of the spindle 110,the movement thereof switches from forward movement to backward movementat the position of 180 degrees in the last rotation of the multiplerotations of the spindle 110 (in the second rotation of the spindle 110in this example), and the cutting tool 130 moves backward toward thesubstantial feed line G. The rotation amount of the spindle during theforward and backward movement of the cutting tool 130 is a rotationamount E of the spindle per vibration of the cutting tool. Further, therotation amount of the spindle during the backward movement of thecutting tool 130 is a rotation amount R of the spindle in the backwardmovement of the cutting tool 130. Here, the rotation amount R of thespindle during the backward movement of the cutting tool 130 is, inother words, the rotation amount of the spindle required from the timewhen the movement of the cutting tool 130 switches from the forwardmovement to the backward movement to the time when the cutting tool 130reaches the substantial feed line G,

For example in a machining program, as a condition for vibration, therotation amount of the spindle during the backward movement can bespecified by a value following R (argument R), and the rotation amountof the spindle per vibration of the cutting tool can be specified inadvance by a value following E (argument E).

The rotation amount E of spindle per vibration of the cutting tool isthe inverse number of the number of vibrations D, and is 2.0 (r/times)in the example in FIG. 8. On the basis of the rotation amount E of thespindle and the amount of feed F at the time when one vibration iscompleted, the return position calculation section 191 calculates aposition of the phase of the spindle corresponding to the rotationamount E of the spindle on the substantial feed line G as a returnposition.

FIG. 8 shows the return positions in two vibrations as direction changepoints B1 and B2 at which the backward movement changes to the forwardmovement. The vibration waveform in FIG. 8 is expressed on a workpiecebasis, and the return positions of the cutting tool 130 at the time whenone vibration is completed are positions of the phase of the spindle onthe substantial feed line G (indicated by a dashed chain line in FIG.9A) obtained by multiplying the angle of one rotation of the spindle(360 degrees) by the rotation amount E of the spindle. As shown in FIG.9B, in the reference example 2, the change point B1 is at a positionwhere the phase of the spindle is 720 degrees. Thereafter, each changepoint is a position on the substantial feed line G with an interval ofan angle corresponding to two rotations of the workpiece W, and in thecase of the reference example 2, the change point B2 on the substantialfeed line G is in a position where the phase of the spindle is 1440degrees. As described above, the return position calculation section 191can calculate each return position on the bases of the rotation amount Eof the spindle and the amount of feed F at the time when one vibrationis completed.

In the reference example 2, the rotation amount R of the spindle in thebackward movement is 0.5 (rotation), thus a rotation of 180 degrees isrequired from the start to the end of the backward movement. Therefore,as shown in FIG. 9B, the direction change point A1, at which the forwardmovement switches to the backward movement, is a phase of the spindle(540 degrees), which is obtained by subtracting the angle correspondingto the rotation amount R of the spindle from the phase of the spindle atthe return position (720 degrees).

In the reference example 2, since the forward movement and the backwardmovement are at the same speed, the forward feed setting section 192sets a line C of 540 degrees of the phase of the spindle as the axis ofsymmetry, sets a point that is line symmetrical with respect to thechange point B1 as the symmetry point B1′, and sets the straight linepassing through 0 degree of the phase of the spindle and the symmetrypoint B1′ as the forward feed movement. The control section 181 outputsa forward feed command for moving the cutting edge along the forwardfeed movement.

As shown in FIG. 9B, the change point A1 is at a position where thephase of the spindle is 540 degrees on a straight line passing through 0degree of the phase of the spindle and the symmetry point B1′. In otherwords, the change point A1 is determined using the amount of feed F, therotation amount R of the spindle in the backward movement and therotation amount E of the spindle at the time when one vibration iscompleted as parameters (change point setting values). The forward feedsetting section 192 sets the forward movement on the basis of the changepoint setting values.

Thereafter, each change point A is at each position of the phase of thespindle, which depends on the rotation amount E of the spindle at thetime when one vibration is completed. Thus, each symmetry point B′ is apoint that is line symmetrical with respect to each change point B withthe axis of symmetry being the line of the phase of the spindle of eachchange point A corresponding to each change point B. In the case of thereference example 2, for example, the symmetry point B2′ is at aposition 360 degrees before 1440 degrees of the phase of the spindle ofthe change point B2. Thus, the symmetry point B2′ is a position wherethe phase of the spindle is 1080 degrees. And, for example, the changepoint A2 is at a position 180 degrees before 1440 degrees of the phaseof the spindle of the change point B2. Thus, the change point A2 is aposition where the phase of the spindle is 1260 degrees.

As shown in FIG. 9C, the direction change point B1 is at a positionwhere the phase of the spindle is 720 degrees. The pulse-like signal Pis a periodic pulse-shaped command output from the return movementsetting section 193 and is a movement command for moving the cuttingedge in the counter-machining direction. The pulse-like signal P has adownwardly convex waveform (indicated by a two-dot chain line in FIG.9C) opposite to the feed direction (vertical axis direction in the graphin FIG. 9C) so that the cutting edge returns from the change point A1 tothe change point B1. The pulse-like signal P is set as a signal outputas a movement command for moving the cutting edge in thecounter-machining direction. The height of the convex shape of thepulse-like signal P can be determined according to the distance betweenA1 and B1 viewed in the feed direction.

By combining the forward feed movement and the return movement, thepulse-like signal P is set so that the cutting edge performs a backwardmovement F″ that connects the change point A1 and the change point B1 asshown in FIG. 9D. And the return movement setting section 193 isconfigured to include the pulse-like signal P.

The pulse-like signal has a period so that the backward movement F″ isstarted from each change point A. The cutting edge starts the backwardmovement F″ from the change point A1 to the change point B1 (a positionwhere the phase of the spindle is 720 degrees) at the timing when thephase of the spindle is 540 degrees by the command of moving in thecounter-machining direction (the downwardly convex portion of thepulse-like signal). When the backward movement F″ intersects with theforward movement F′ at the change point B1, the chip is segmented.

On the other hand, if there is no command of moving in thecounter-machining direction from the return movement setting section193, the cutting edge simply moves from the change point B to the changepoint A along the forward feed movement. Therefore, as shown in FIG.10A, a forward movement F′ from the change point B1 to the change pointA2 (a position where the phase of the spindle is 1260 degrees) isperformed.

Next, movement in the counter-machining direction is commanded at thetiming when the phase of the spindle is 1260 degrees, and as shown inFIG. 10B, a backward movement F″ passing through the change point A2 andthe change point B2 (a position where the phase of the spindle is 1440degrees) is performed. When the backward movement F″ intersects with theforward movement F′ at the change point B2, the chip is segmented.

As described above, the cutting tool 130 can be fed with theabove-mentioned vibration by combining the forward feed movement and thereturn movement. In particular, by the return position calculationsection 191, the forward feed setting section 192 and the returnmovement setting section 193, the vibration of the cutting tool 130 canbe automatically set according to the predetermined amount of feed F.Thus, it is possible to easily perform cutting with the vibrationaccording to the amount of feed F.

In the reference examples 1 and 2 described above, the spindle 110 isrotated and fed in the Z-axis direction. However, the present inventionis not limited to these examples. The same effect also can be obtained,for example in cases where the spindle 110 is rotated and the cuttingtool 130 is fed in the Z-axis direction, the cutting tool 130 is rotatedand the spindle 110 is fed in the Z-axis direction, the spindle 110 isfixed and the cutting tool 130 is rotated and fed in the Z-axisdirection, and the like. The Z-axis direction feeding mechanismcorresponds to the feeding means of the present invention. In addition,the rotation amount E of the spindle per vibration of the cutting toolin the reference example 2 may be set not only to an integral number ofrotations such as two rotations and three rotations, but also to anumber corresponding to a rotation angle exceeding one rotation (360degrees).

The pulse-like signal P of the return movement setting section 193 maybe a signal or the like that repeats a command for moving the cuttingtool 130 to the phase of the spindle of the change point A in themachining direction and a command for moving the cutting tool 130 fromthe phase of the spindle of the change point A in the counter-machiningdirection. In this case, the forward feed setting section 192 can setthe forward feed movement so that the forward feed movement is acombination of a movement of the cutting edge in the machining directionbased on the pulse-like signal P (the movement in the machiningdirection by the command for moving the cutting tool to the phase of thespindle of the change point A in the machining direction) and a movementin the machining direction by a predetermined forward feed command. Thepredetermined forward feed command can be, for example, a forward feedcommand for moving the cutting edge onto the substantial feed line G.

Particularly, FIG. 11A shows an example where the number of vibrations Dis 0.5 (times/r). When the amount of feed F is specified, a substantialfeed line G (indicated by a dashed line in the figure, which correspondsto the feed line of the cutting tool of the present invention) isdetermined. Further, on the basis of the rotation amount E of thespindle per vibration of the cutting tool and the amount of feed F, thereturn position (change point BD on the substantial feed line G iscalculated.

In a case where the rotation amount R of the spindle in the backwardmovement of the cutting tool 130 is 0.5 (rotation), the direction changepoint A1 at which the forward movement switches to the backward movementis at 540 degrees of the phase of the spindle. The line C of 540 degreesof the phase of the spindle is set as the axis of symmetry, and asymmetrical point B1′, which is line symmetrical with respect to thechange point B1, is set. Then, the straight line passing through 0degree of the phase of the spindle and the symmetrical point BP is setas forward feed movement.

If the predetermined forward feed command is a forward feed command formoving the cutting edge onto the substantial feed line G, there is apositional difference C′ between the substantial feed line G and thechange point A1 at a position where the phase of the spindle is 540degrees as shown in FIG. 11B. The pulse-like signal P is set to have anupwardly convex waveform (indicated by a two-dot chain line in FIG. 11C)which is forwardly directed in the feed direction (vertical axisdirection of the graph in FIG. 11B) so as to return the cutting edge tothe substantial feed line G after obtaining the positional differenceC′.

The forward feed setting section 192 sets the forward feed movement(indicated by F′) by combining the movement in the machining directionby a command of the pulse-like signal P, which is for moving the cuttingedge in the machining direction to 540 degrees of the phase of thespindle at the change point A1, and the movement in the machiningdirection determined by the amount of feed F (substantial feed line G).

The pulse-like signal P has a period so that a straight line passingthrough 0 degree of the phase of the spindle and the symmetry point B1′starts from 0 degree of the phase of the spindle. The cutting edgestarts the forward movement F′ from 0 degree of the phase of the spindleto the change point A1 at the timing when the phase of the spindle is 0degree, and starts the backward movement F″ from the change point A1 onthe forward movement F′ at the timing when the phase of the spindle is540 degrees. Thereafter, the command for moving the cutting edge in themachining direction from the phase of the spindle of the change point Bto the phase of the spindle of the change point A and the command formoving the cutting edge in the counter-machining direction from thephase of the spindle of the change point A to the phase of the spindleof the change point B are repeated by the pulse-like signal P.

The movement in the machining direction by the command of the pulse-likesignal P for moving the cutting edge in the machining direction and themovement in the machining direction by the forward feed command can bearbitrary movements as long as they are combined to be the forward feedmovement. The substantial feed line G is same as a line determined bythe amount of feed F in general cutting without above-mentionedvibration (that is conventional cutting). Therefore, by setting theforward feed command as a forward feed command for moving the cuttingedge onto the substantial feed line G, the forward movement F′ can beobtained by adding the pulse-like signal P to the conventional cutting.

In the reference example 3, an example where the change point A1 isdetermined from the amount of feed F, the rotation amount R of thespindle in the backward movement, and the rotation amount E of thespindle at the time when one vibration is completed is described.However, the pulse-like signal P can also be naturally applied to a casewhere the change point A1 is determined from the amount of feed F, theamplitude feed ratio Q, and the number of vibrations D.

PRESENT EXAMPLE

Further, the pulse-like signal P of the return movement setting section193 may be formed in sine waveform.

Particularly, FIG. 12A shows an example where the number of vibrations Dis 1.5 (times/r). When the amount of feed F is specified, a substantialfeed line G (indicated by a dashed line in the figure, which correspondsto the feed line of the cutting tool of the present invention) isdetermined. Further, in a case where the number of vibrations D is 1.5(times/r), the return position (change point BD on the substantial feedline G is a position where the phase of the spindle is 240 degrees, andthe direction change point A1 at which the forward movement switches tothe backward movement is at 120 degrees of the phase of the spindle.

Similar to the reference example 3, if the predetermined forward feedcommand is a forward feed command for moving the cutting edge onto thesubstantial feed line G, there is a positional difference C′ between thesubstantial feed line G and the change point A1 at a position where thephase of the spindle is 120 degrees as shown in FIG. 12B. The pulse-likesignal P is set to have a sign waveform (indicated by a two-dot chainline in FIG. 12C) so as to return the cutting edge to the substantialfeed line G after obtaining the positional difference C′.

In the present example, the substantial feed line G and a curve of sinewaveform are combined. The α degrees of the phase of the spindle at theinflection point a1 (the point at which the sine curve changes fromconvex to concave (the point at which the curvature of the curve changesfrom positive to negative)) shown in FIG. 12C is set to a valuedifferent from 120 degrees of the phase of the spindle of the changepoint A1 (for example, a value smaller than 120 degrees) shown in FIG.12A. In this way, the cutting edge reaches the top of the convex shapeon the sine curve at the change point A1 (at 120 degrees of the phase ofthe spindle) and then heads toward the bottom of the concave shape.Further, the β degrees of the phase of the spindle at the inflectionpoint b1 (the point at which the sine curve changes from concave toconvex (the point at which the curvature of the curve changes fromnegative to positive)) shown in FIG. 12C is set to a value differentfrom 240 degrees of the phase of the spindle of the change point B1 (forexample, a value larger than 120 degrees) shown in FIG. 12A. In thisway, the cutting edge reaches the bottom of the concave shape on thesine curve at the change point B1 (at 240 degrees of the phase of thespindle) and then heads toward the top of the convex shape.

The forward feed setting section 192 sets the forward feed movement(indicated by F′ in FIG. 12) by combining the movement in the machiningdirection by a command, which is for moving the cutting edge in themachining direction to 120 degrees of the phase of the spindle at thechange point A1 of this sine waveform, and the movement in the machiningdirection determined by the amount of feed F (substantial feed line G).

The pulse-like signal P has a period so that the concave shape of thissine waveform starts from a position which is (β-240) degrees later thanthe 0 degree of the phase of the spindle. At the timing when the phaseof the spindle is 0 degree, the cutting edge starts the forward movementF′ (the movement in the right part of the concave shape (movement in theleft part of the convex shape)) from 0 degree of the phase of thespindle to the change point A1, and starts the backward movement F″ fromthe change point A1 on the forward movement F′ at the timing when thephase of the spindle is 120 degrees. This F′ reaches the bottom of theconcave shape on the sine curve at the 240 degrees of the phase of thespindle at the change point B1. Thereafter, the command for moving thecutting edge in the machining direction from the phase of the spindle ofthe change point B to the phase of the spindle of the change point A andthe command for moving the cutting edge in the counter-machiningdirection from the phase of the spindle of the change point A to thephase of the spindle of the change point B are repeated by thepulse-like signal P.

REFERENCE SIGNS LIST

-   100 machine tool-   110 spindle-   110A spindle headstock-   120 chuck-   130 cutting tool-   130A tool post-   150 X-axis direction feeding mechanism-   151 base-   152 X-axis direction guide rail-   153 X-axis direction feeding table-   155 linear servomotor-   155 a mover-   155 b stator-   160 Z-axis direction feeding mechanism-   161 base-   162 Z-axis direction guide rail-   163 Z-axis direction feeding table-   165 linear servomotor-   165 a mover-   165 b stator-   180 control device-   181 control section-   182 numerical value setting section-   183 storage section-   190 motor control section-   191 return position calculation section-   192 forward feed setting section-   193 return movement setting section

1. A control device for a machine tool comprising: a feeding means forfeeding a relatively rotating cutting tool and material; and a controlmeans for controlling the rotation and operation of the feeding means,the control means performing control such that cutting is performed withvibrating the cutting tool relative to the material by combining aforward feed movement in a machining direction, in which the cuttingtool machines the material, and a return movement in a counter-machiningdirection different from the machining direction, wherein the controldevice includes: a return position calculation means for calculating areturn position of the cutting tool at a time when one vibration iscompleted on the basis of a number of vibrations and an amount of feedthat are predetermined for one rotation of the cutting tool or thematerial; a forward feed setting means for setting a forward feedmovement on the basis of a change point setting value that determines achange point from the machining direction to the counter-machiningdirection, and for making the cutting tool reach the determined changepoint; and a return movement setting means for setting a pulse-likesignal that is output as a command for the return movement so that thecutting tool reaches the calculated return position at time when onevibration is completed, wherein the return movement setting means sets apulse signal including a command for moving a cutting tool in themachining direction and a command for the return movement, and theforward feed setting means makes the cutting tool reach the change pointby combining the movement in the machining direction on the basis of thereturn movement setting means and the forward feed movement, and whereinthe pulse signal is formed in sine waveform with an inflection point,and a phase of the inflection point for making the cutting tool reachthe change point is set to a value different from a phase of the changepoint.
 2. The control device for a machine tool according to claim 1,wherein the number of vibrations is one or more.
 3. The control devicefor a machine tool according to claim 1, wherein the number ofvibrations is less than one.
 4. A machine tool comprising the controldevice for a machine tool according to claim
 1. 5. A machine toolcomprising the control device for a machine tool according to claim 2.6. A machine tool comprising the control device for a machine toolaccording to claim 3.